1. FIELD OF THE INVENTION
This invention relates to a method and apparatus for measuring the remaining charge of various galvanic cells, and more particularly to a method and apparatus for simple yet accurate measurement of the remaining charge of various galvanic cells, inclusive of primary or secondary cells, or the amount of electricity with which the galvanic cell has been charged.
2. DESCRIPTION OF THE PRIOR ART
As a way of finding out the remaining charge of a given galvanic cell, the measurement of terminal voltage, impedance, ect. of the galvanic cell has been generally resorted to. These quantities vary very slightly with variation in the remaining charge of the galvanic cell within the range of normal use (1.6 to 0.9 V, 1 to 2 .OMEGA. (at 31.2 Hz) in a manganese dry cell (Ever Ready SP11), for example). Moreover, these quantities vary greatly depending on the presence or absence of load or on how long the cell has been released from load. Thus, they cannot be relied on to indicate the remaining charge with accuracy. More often than not the dependence of impedence upon charge lacks linearity as by possessing a minimum value, for example. In the case of the lead acid battery which is the secondary battery currently in most popular use, the remaining charge is found by measuring the specific gravity of the aqueous sulfuric acid solution used as the electrolytic solution therein. This method inevitably requires a prescribed amount of the dilute sulfuric acid to be removed as a sample from the battery, making the measurement quite inconvenient. Incorporation in the battery of a float or a refractance measuring cell as means of measurement has been proposed. The former version has the disadvantage that the mechanism of measurement is vulnerable to vibration, the float is liable to get caught, and the float tends to gather bubbles possibly to the extent of jeopardizing the accuracy of measurement. The latter version has the disadvantage that the accuracy of measurement is impaired by the dirt adhering to the cell and the instable intensity of the light source. In another method, measurement of the concentration of sulfuric acid solution is effected using a second miniature cell disposed within the battery. This method is disadvantageous in that the battery has a complicated construction and the second miniature cell itself is susceptible to deterioration.